Rankine cycle system and method

ABSTRACT

A Rankine cycle waste heat recovery system uses a receiver with a maximum liquid working fluid level lower than the minimum liquid working fluid level of a sub-cooler of the waste heat recovery system. The receiver may have a position that is physically lower than the sub-cooler&#39;s position. A valve controls transfer of fluid between several of the components in the waste heat recovery system, especially from the receiver to the sub-cooler. The system may also have an associated control module.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 61/426,872, filed on Dec. 23, 2010 which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to a waste heat recovery system using a Rankinecycle. The waste heat recovery system uses a receiver with a fluid levellower than the fluid level of a sub-cooler of the waste heat recoverysystem. The disclosure also teaches a method of using the describedconfiguration.

BACKGROUND

There is typically little space available in an engine compartment orchamber. Because of the need for various reservoirs, filters, and otherelements or components to sit at or above a top portion of an engine,space at or above a top portion of an engine is typically less availablethan space along side an engine or below an engine. In an engine systemusing a Rankine cycle, a receiver in existing systems sits higher thanthe sub-cooler, which permits gravity feeding of the sub-cooler.However, because engines in some applications occupy a high position inan engine compartment or cavity, it may be difficult for a receiver tobe in an optimal position.

SUMMARY

This disclosure provides a fluid management system for a Rankine cyclewaste heat recovery system for an internal combustion engine. The fluidmanagement system comprises a fluid circuit, a condenser positionedalong the fluid circuit, a sub-cooler fluidly connected to the condenserand containing a liquid working fluid, and a receiver fluidly connectedto the sub-cooler and containing the liquid working fluid. A level ofthe liquid working fluid in the receiver is lower than a level of theliquid working fluid in the sub-cooler throughout all operatingconditions.

This disclosure also provides a waste heat recovery system for aninternal combustion engine. The system comprises a working fluidcircuit. The circuit includes a cooled condenser receiving a vaporizedworking fluid and operable to change the state of the vaporized workingfluid to a liquid working fluid. A sub-cooler is fluidly connected tothe condenser and receives the liquid working fluid. A pump is fluidlyconnected to the sub-cooler and operable to move the liquid workingfluid from the sub-cooler. A heat exchanger is fluidly connected to apump to receive the liquid working fluid and operable to transfer heatfrom a heat source to the liquid working fluid to convert the liquidworking fluid to the vaporized working fluid, wherein the vaporizedworking fluid is at a high pressure. An energy conversion device isfluidly connected to the heat exchanger and operable to convert thehigh-pressure vaporized working fluid received from the heat exchangerto energy. The system also comprises a fluid management circuit fluidlyconnected to the working fluid circuit. The fluid management circuitincludes a conversion device bypass valve fluidly connected to the heatexchanger in parallel to the energy conversion. A receiver is fluidlyconnected to the conversion device bypass valve. The receiver is placedat a physical location where the maximum liquid working fluid level inthe receiver is lower than the minimum liquid working fluid in thecondenser and the sub-cooler. The conversion device bypass valve isoperable to fluidly connect the heat exchanger to the receiver,simultaneously disconnecting a direct path to the condenser from theheat exchanger and the receiver. The vaporized working fluid flowingfrom the heat exchanger forces the liquid working fluid to flow from thereceiver to the sub-cooler.

This disclosure also provides a valve configuration for a Rankine cyclewaste heat recovery system. The valve configuration comprises a heatexchanger, wherein the heat exchanger is a source of vaporized workingfluid. The valve configuration also comprises a condenser, a sub-coolerfluidly connected to the condenser, a receiver fluidly connected to thesub-cooler, and a valve. The valve has a first position such that thevalve fluidly connects the receiver to the condenser. The valve has asecond position such that the valve fluidly connects the heat exchangerto the receiver. The valve has a third position such that the valvefluidly connects the heat exchanger to the condenser.

This disclosure also provides a waste heat management system, comprisinga sub-cooler containing a liquid working fluid. The liquid working fluidin the sub-cooler has a first level. A receiver is fluidly connected tothe sub-cooler and contains the liquid working fluid. The liquid workingfluid in the receiver has a second level. A valve is fluidly connectedto the receiver. The first level is higher than the second level. Thevalve is selectively operable to deliver vaporized working fluid to thereceiver to apply pressure to the liquid working fluid in the receiverto force the liquid working fluid in the receiver to flow into thesub-cooler.

This disclosure also provides a method of controlling fluid flow througha waste heat recovery system. The method comprises generating vaporizedfluid in a working fluid circuit from a liquid working fluid located inthe working fluid circuit. The liquid working fluid has a level. Themethod also comprises providing the vaporized fluid to a working fluidmanagement circuit connected in parallel to the working fluid circuit.The method also comprises determining that the level of the liquidworking fluid in the working fluid circuit is different from anoperationally desirable level. The method also comprises allowing thevaporized fluid to flow through the working fluid management circuitapplying the vaporized fluid to the working fluid management circuit toforce liquid working fluid in the working fluid management circuit toflow from the working fluid management circuit into the working fluidcircuit, to change the level of the liquid working fluid in the workingfluid circuit. The method also comprises terminating the flow ofvaporized fluid through the working fluid management circuit when theliquid working fluid in the working fluid circuit has reached anoperationally desirable level.

Advantages and features of the embodiments of this disclosure willbecome more apparent from the following detailed description ofexemplary embodiments when viewed in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of a conventional Rankine cycle wasteheat recovery system.

FIG. 2 is a simplified schematic of a Rankine cycle waste heat recoverysystem in accordance with an exemplary embodiment of the presentdisclosure.

FIG. 3A is a schematic view of a conversion device bypass valve of theRankine cycle waste heat recovery system of FIG. 2 in a first position.

FIG. 3B is a schematic view of a conversion device bypass valve of theRankine cycle waste heat recovery system of FIG. 2 in a second position.

FIG. 3C is a schematic view of a conversion device bypass valve of theRankine cycle waste heat recovery system of FIG. 2 in a third position.

FIG. 4 is a flow diagram of the control configuration of FIG. 2.

DETAILED DESCRIPTION

Applications of a Rankine cycle, which includes an organic Rankinecycle, for increasing the thermal efficiency of internal combustionengines are increasing. A Rankine cycle can convert a portion of heatenergy that normally would be wasted in an internal combustion engine,such as exhaust gas heat energy and other engine heat sources (e.g.,engine oil, exhaust gas, charge gas, water jackets), into energy thatcan perform useful work. In converting the captured heat energy intouseful work, a portion of the waste heat energy can be recovered toenhance an engine's efficiency.

Turning now to the figures, shown in FIG. 1 is a conventional Rankinecycle waste heat recovery system 10, or WHR system 10. WHR system 10includes a working fluid circuit 12, which includes a heat exchangeportion 14, and an energy capture portion 16.

Working fluid circuit 12 includes a sub-cooler 18, which may connect toa condenser 20 by way of a base plate 22. Connected to sub-cooler 18 byway of a receiver conduit 24 is a receiver 26. A pump conduit 28connects a working fluid pump 30 with receiver 26. A heat exchangerconduit 32 connects pump 30 with a heat exchanger 34 of heat exchangeportion 14.

Heat exchange portion 14 includes at least one heat exchanger, one ofwhich may be a boiler heat exchanger 34. Though not shown, there may beadditional heat exchangers between pump 30 and boiler heat exchanger 34.These additional heat exchangers may be any one of a plurality of heatexchangers, such as an exhaust heat exchanger, a pre-charge air coolerheat exchanger, a recuperator, or other heat exchangers that may benefitfrom an exchange of heat with the relatively cool liquid working fluidcoming from working fluid circuit 12. These heat exchangers may be inseries, parallel, or a combination of series and parallel. Boiler heatexchanger 34 may be an EGR boiler/superheater. In this example, boilerheat exchanger 34 would connect to the upstream side of an exhaust gasrecirculation (EGR) system 42 by way of an EGR system conduit 38. Boilerheat exchanger 34 may also connect to the downstream side of EGR system42 by way of an EGR conduit 40. A conversion device conduit 44 connectsto a conversion device 46 of energy capture portion 16.

Conversion device 46 may connect to an auxiliary system 48. A condenserconduit 50 connects conversion device 46 with condenser 20 of workingfluid circuit 12.

WHR system 10 works as follows. Sub-cooler 18 receives condensed workingfluid from condenser 20 by way of base plate 22. Base plate 22 containsone or more fluid paths to connect condenser 20 to sub-cooler 18fluidly. Condenser 20 may fluidly connect to sub-cooler 18 by conduitsor other devices or mechanisms. Condenser 20 and sub-cooler 18 may alsobe a single integral unit. Liquid working fluid flows from sub-cooler 18through receiver conduit 24 to receiver 26. Receiver 26 may act as areservoir for liquid working fluid. Working fluid pump 30 pumps or pullsliquid working fluid from receiver 26 via pump conduit 28. Pump 30 thenmoves liquid working fluid through heat exchanger conduit 32 to boilerheat exchanger 34. Boiler heat exchanger 34 receives hot exhaust gasfrom EGR system 42 through EGR system conduit 38. Heat transfers fromthe hot exhaust gas to the liquid working fluid. The temperature of thehot exhaust gas is sufficient to cause the liquid working fluid receivedfrom heat exchanger conduit 32 to boil, turning the liquid working fluidinto a high-pressure vapor. The heat transfer from the hot exhaust gasto the liquid working fluid cools the hot exhaust gas and the exhaustgas returns through EGR conduit 40 to EGR system 42.

High-pressure vaporized working fluid now flows through conversiondevice conduit 44 to conversion device 46. The vaporized working fluidcools and loses energy, which translates to decreased pressure, as ittravels through conversion device 46. Conversion device 46 may drive anauxiliary system 48. The vaporized working fluid next flows throughcondenser conduit 50 to condenser 20. Condenser 20 may contain aplurality of passages through which vaporized working fluid and liquidworking fluid may move. Cooling air or fluid flows across and possiblythrough condenser 20, passing over the plurality of passageways anddecreasing the temperature of the vaporized working fluid to the pointwhere the vaporized working fluid condenses to a liquid. The warm liquidworking fluid flows through base plate 22 to return to sub-cooler 18,where the liquid working fluid may receive additional cooling fromcooling air or fluid before repeating the above-described cycle.

The working fluid described in the configuration shown in FIG. 1 and insubsequent figures can be a non-organic or an organic working fluid.Some examples of working fluid are Genetron® R-245fa from Honeywell,Therminol®, Dowtherm J™ from Dow Chemical Co., Fluorinol® from AmericanNickeloid, toluene, dodecane, isododecane, methylundecane, neopentane,octane, water/methanol mixtures, and steam.

Shown in FIG. 2 is an exemplary embodiment of the present disclosure. ARankine cycle waste heat recovery system 100 that includes a workingfluid circuit 111, which has, among other things, a heat exchangeportion 14 and an energy capture portion 116, and, more importantly, aworking fluid management system or circuit 112 fluidly connected toworking fluid circuit 111 to achieve one or more operational andfunctional benefits and advantages described herein. Elements having thesame number as the elements described in FIG. 1 behave as described inthe previous discussion of FIG. 1. Discussion of these elements is onlyfor clarity in discussion of the exemplary embodiment.

Heat exchange portion 14 includes at least one heat exchanger 34, whichconnects to working fluid pump 30 downstream from working fluid pump 30.Heat exchange circuit 14 also includes an EGR system 42, which is bothupstream and downstream from heat exchanger 34, discussed in more detailhereinbelow. Downstream from heat exchange circuit 14 is an energycapture portion 116 and fluid management system 112. Heat exchangecircuit 14 connects to an upstream side of a conversion device bypassvalve 70 of fluid management system 112.

Energy capture portion 116 includes at least one energy conversiondevice 46, which may connect to an auxiliary device. Only a part ofenergy capture portion 116 appears in FIG. 2. Energy conversion device46 of Rankine cycle WHR system 100 is capable of producing additionalwork or transferring energy to another device or system. For example,energy conversion device 46 can be a turbine that rotates as a result ofexpanding working fluid vapor to provide additional work, which can befed into the engine's driveline to supplement the engine's power eithermechanically or electrically (e.g., by turning a generator), or it canbe used to power electrical devices, parasitic or a storage battery (notshown). Alternatively, the energy conversion device can be used totransfer energy from one system to another system (e.g., to transferheat energy from WHR system 100 to a fluid for a heating system).

Energy capture portion 116 connects to heat exchange circuit 14downstream from heat exchange circuit 14. More specifically, energycapture portion 116 connects to heat exchanger 34 downstream from heatexchanger 34. Energy capture portion 116 connects to an upstream side ofcondenser 20.

Working fluid management circuit 112 includes a receiver 126, conversiondevice bypass valve 70, and a shutoff valve 58. Sub-cooler 18 andcondenser 20 provide functions for both working fluid circuit 111 andworking fluid management circuit 112 and may be considered part of theopposite circuit when describing transfer of fluid and vapor. Receiver126 is connected to condenser 20 and sub-cooler 18, which may beconsidered either upstream or downstream of receiver 126, as will beexplained in more detail hereinbelow. Upstream of receiver 126 isconversion device bypass valve 70. Connected downstream from sub-cooler18 is working fluid pump 30.

Positioned within receiver 126 is a dip tube 52. Dip tube 52 extendsbelow the surface of a liquid working fluid 54. A dip tube conduit 56connects dip tube 52 to shutoff valve 58. A shutoff valve conduit 60connects shutoff valve 58 to a base plate 222. Base plate 222 serves toconnect condenser 20 to sub-cooler 18 fluidly as well as providing alocation for liquid working fluid level sensor 62. Because receiver 126connects to base plate 222, sub-cooler 18 connects directly to anupstream side of working fluid pump 30 by way of pump conduit 28.Receiver 126 is placed or positioned relative to sub-cooler 18 so thatwhen liquid working fluid 54 is at a maximum level in receiver 126, thelevel of liquid working fluid 54 in receiver 126 is lower than theminimum level of liquid working fluid 54 in sub-cooler 18. Thus,throughout operation of WHR system 100, the top surface or level of theworking fluid in receiver 126 will always be vertically lower than thetop surface or level of working fluid in sub-cooler 18, under alloperating conditions. One method of meeting this condition is to placereceiver 126 so that it is physically located lower than both condenser20 and sub-cooler 18.

Heat exchanger conduit 32 connects a downstream side of pump 30 toboiler heat exchanger 34, which functions in a manner previouslydescribed. An outlet conduit 64 connects a downstream side of boilerheat exchanger 34 to a junction 66. A conversion device bypass conduit68 connects junction 66 to an upstream side of conversion device bypassvalve 70, which is part of working fluid management system 112. Aconversion device conduit 72 connects a downstream side of junction 66to expander conversion device 46, which may drive auxiliary system 48and connects to an upstream side of condenser 20 by way of condenserconduit 50. Since conversion device bypass conduit 68 and conversiondevice conduit 72 both connect to junction 66, they fluidly connect tojunction 66 in parallel to each other. Conversion device bypass valve 70connects to an upstream side of receiver 126 by way of receiver conduit74. Conversion device bypass valve 70 also connects to an upstream sideof condenser 18 by way of a vent and bypass conduit 76. As will be seen,conversion device bypass valve 70 is in a configuration that providescertain operational benefits to WHR system 100.

WHR system 100 works as follows. Sub-cooler 18 stores liquid workingfluid 54. Pump 30 operates to pull liquid working fluid 54 fromsub-cooler 18 by way of pump conduit 28. Pump 30 then pushes liquidworking fluid 54 through heat exchanger conduit 32 to boiler heatexchanger 34. Boiler heat exchanger 34 works as previously described.High-pressure vaporized working fluid 54 exits boiler heat exchanger 34through outlet conduit 64, traveling to junction 66. The vaporizedworking fluid then has the opportunity to travel through two paths, aswill be seen.

Vaporized working fluid travels from junction 66 through conversiondevice conduit 72 to conversion device 46, which works as previouslydescribed. From conversion device 46, vaporized working fluid travelsthrough condenser conduit 50 to return to condenser 20, wherein coolingair or liquid flowing through condenser 20 causes the temperature of thevaporized working fluid to decrease so that the vaporized working fluidcondenses and becomes liquid working fluid 54. Liquid working fluid 54returns to sub-cooler 18 by way of base plate 222, which has fluidpassages (not shown) formed therein.

Returning to junction 66, vaporized working fluid can also flow throughconversion device bypass conduit 68 to conversion device bypass valve 70when conversion device bypass valve 70 permits such flow, as will bedescribed in more detail hereinbelow. Conversion device bypass valve 70has three positions. These three positions connect to various elementsof WHR system 100, as has been previously described, in specificconfigurations. In a first position, shown in FIG. 3A, conversion devicebypass valve 70 connects receiver conduit 74 with vent and bypassconduit 76. Conversion device bypass valve 70 blocks conversion devicebypass conduit 68 when conversion device bypass valve 70 is in the firstposition. In this configuration, which is the position bypass valve 70is likely to occupy for most of its operational time, provides ventingfor receiver 126 to permit vapor to flow between receiver 126 tocondenser 20.

Because of the position of receiver 126 and the absence of pressure inreceiver conduit 74 and the upper portion of receiver 126, liquidworking fluid 54 may drain by gravity into receiver 126 through shutoffvalve conduit 60, shutoff valve 58, dip tube conduit 56 and then diptube 52, if there is excess liquid working fluid in sub-cooler 18 andcondenser 20. Thus, while receiver 126 is fluidly upstream of sub-cooler18 and condenser 20, in some circumstances it may be downstream ofsub-cooler 18 as fluid drains from sub-cooler 18 and condenser 20 by theforce of gravity into receiver 126. Shutoff valve 58 is normally openduring operation of WHR system 100. However, shutoff valve 58 may closeduring system shutdown to isolate receiver 126 and during certainoperating modes to increase the level of liquid working fluid 54 insub-cooler 18 and condenser 20. The position of receiver 126 isbeneficial to placement of receiver 126 in a vehicle. As previouslynoted, space in an engine compartment or chamber (not shown) istypically unavailable in many areas, particularly near the top portionof such a compartment or chamber. Because receiver 126 is positionedlower than the other components of WHR system 100, it is easier toincorporate WHR system 100 in an engine system.

In a second position, shown in FIG. 3B, conversion device bypass valve70 connects conversion device bypass conduit 68 with receiver conduit74. Conversion device bypass valve 70 blocks vent and bypass conduit 76when conversion device bypass valve 70 is in the second position. In thesecond position, vaporized working fluid flows through receiver conduit74 into receiver 126. Because the vaporized working fluid is underpressure, and because dip tube 52 is below the surface of liquid workingfluid 54, the vaporized working fluid forces liquid working fluid 54into dip tube 52. From dip tube 52, liquid working fluid 54 flows intodip tube conduit 56, through shutoff valve 58, through shutoff valveconduit 60, and then into base plate 222, where liquid working fluid 54then flows to sub-cooler 18 to raise the level of liquid working fluid54 in sub-cooler 18. Once the level of liquid working fluid 54 is at anappropriate or operationally desirable level, which working fluid levelsensor 62 determines by sensing or detecting a parameter of the workingfluid, for example the level, temperature or pressure of the workingfluid, then conversion device bypass valve 70 will return to either thefirst position or a third position, described hereinbelow, terminatingflow of vaporized working fluid through working fluid management circuit112.

It should be apparent from the foregoing description that working fluidmanagement circuit 112 operates to adjust the level of the liquidworking fluid in the working fluid circuit 111. When the level of theliquid working fluid is too high, which may be determined one or moresensors, for example, sensor 62 or sensor 85, fluid may drain fromworking fluid circuit 111 through valve 58 of working fluid managementcircuit 112 into working fluid management circuit 112. Conversely, whenthe level of the liquid working fluid in working fluid circuit 111 istoo low, which one or more sensors, for example, sensor 62 or sensor 85,then conversion device bypass valve 70 in fluid management circuit 112is set to force liquid working fluid from working fluid managementcircuit 112 to working fluid circuit 111, increasing the level of theworking fluid in working fluid circuit 111.

In the third position, shown in FIG. 3C, conversion device bypass valve70 connects conversion device bypass conduit 68 with vent and bypassconduit 76. Conversion device bypass valve 70 blocks receiver conduit 74when conversion device bypass valve 70 is in the third position. Onebenefit to this third position is that pressure spikes, peaks ortransients resulting from the expansion of working fluid as it vaporizesmay bypass conversion device 46, decreasing the stress on conversiondevice 46. Bypassing conversion device 46 means that high pressurevaporized working fluid is diverted around conversion device 46 orrouted to condenser 20 directly, increasing the heat load on condenser20 and increasing the heat rejection requirement for condenser 20. Theincreased pressure and temperature in condenser 20, which fluidlyconnects to sub-cooler 18, causes liquid working fluid 54 to be underincreased or greater pressure as it flows through pump conduit 28 topump 30. The increased pressure of liquid working fluid 54 as it flowstoward pump 30 provides benefits, which includes increasing thecavitation margin of the pump by increasing the working fluidsub-cooling (the degrees of temperature below the saturation temperaturefor the measured pressure), which assists pump 30 in maintaining prime,or the ability to move fluid.

Though the description of conversion device bypass valve 70 has been interms of discrete positions, conversion device bypass valve 70 mayoperate as a proportional valve movable to partial open/closed positionsor may be modulated or cycled rapidly between positions, also calledbinary operation or modulation. Thus, conversion device bypass valve 70may operate in a way to gain the benefit of all three positions bycycling through the positions quickly, with a dwell time in any oneposition of tenths of second.

WHR system 100 has a number of functions that an automatic system maycontrol. Referring again to FIG. 2, in addition to the previouslydescribed systems and components is a control system 78. Control system78 includes a plurality of sensors and a control module 80. Controlmodule 80 may be an electronic control unit or electronic control module(ECM) that monitors the performance of an internal combustion engine inwhich WHR system 100 is located or may monitor other vehicle conditions.Control module 80 may also be either a single unit or multiple controlunits that may communicate with each other or with yet another controlmodule or unit. Control module 80 may also be a digital or analogcircuit.

A plurality of sensors 82 associated with pump conduit 28 sendstemperature and pressure information to control module 80. Note thatwhile lines are shown in FIG. 2 to denote connections, such connectionsmay be via wire, cable, fiber optics, wireless, power path and othertechniques for transmitting a signal from a sensor and receiving thatsignal. Control module 80 also receives temperature and pressureinformation from sensors 84 associated with conversion device 46.Working fluid level sensor 62 also transmits data to control module 80.Control module 80 may receive inputs from other sensors to aid inrefined control of WHR system 100.

In addition to receiving sensor inputs, control module 80 may sendsignals to one or more devices for control of those devices. Forexample, control module 80 connects to shutoff valve 58 and toconversion device bypass valve 70 to operate those valves, using theinformation gathered from the plurality of sensors described above andpossibly information stored within control module 80 or other databasesor storage devices.

Control module 80 may include a processor or the equivalent and modulesin the form of software or routines stored on electronically readablemedia such as memory, which the processor of control module 80 executes.For example, instructions for carrying out the processes shown in FIG. 2may be stored integrally with control module 80 or stored elsewhere, butaccessible by control module 80. In alternative embodiments, portions ofcontrol module 80 may include electronic circuits for performing some orall of the processing. These electronic circuits may be analog ordigital. These modules may include a combination of software, electroniccircuits and microprocessor based components. Control module 80 may be amodule specifically designed for this application. Control module 80 mayreceive data indicative of engine performance and exhaust gascomposition including, but not limited to, engine position sensor data,speed sensor data, exhaust mass flow sensor data, fuel rate data,pressure and temperature sensor data from one or more locations of anengine (not shown) and an associated exhaust aftertreatment system (notshown), data regarding requested power, and other data. Control module80 may then generate control signals and output these signals to controlelements of WHR system 100, an engine, an associated aftertreatmentsystem, and other systems and devices associated with a vehicle or othersystem using the engine. Note that some engines incorporating WHR system100 may be in a fixed location, providing primary or backup power for astationary facility. Some engines incorporating WHR system 100 may be ina marine application, thus the term vehicle should be considered a broadterm covering any mobile application.

Referring now to FIG. 4, a flow chart is shown that describes a processthat may be used to determine the various valve positions of thethree-way conversion device bypass valve 70. The flow chart uses theterm “turbine” as an exemplary embodiment of a conversion device. Theprocess begins with step 210, where control module 80 receives signalsfrom various sensors provided in WHR system 100, particularly sensors 84that measure parameters of conversion device 46. The received signalsare used to determine whether the estimated conversion device power isgreater than a maximum threshold value in decision step 212. If theestimated conversion device power is greater than the maximum thresholdvalue, the process moves to step 214 where control module 80 will moveconversion device bypass valve 70 to the third position. As previouslydescribed, when conversion device bypass valve 70 is in the thirdposition some of the high-pressure vaporized working fluid is bypassedaround conversion device 46 by way of conversion device bypass conduit68 and vent and bypass conduit 76, thus decreasing the amount ofvaporized working fluid moving through conversion device 46, therebydecreasing the amount of energy imparted to conversion device 46. Theprocess may move to decision step 216 next.

At step 216, the control module determines whether the engine (notshown) and thus WHR system 100 is still operating. If WHR system 100 isstill operating, then the process will return to step 210. If WHR system100 is no longer operating, then the process will move to a terminationstep 218. This description is confined to a limited portion of theoperation of an engine. The entire process may be much more complex andinvolve many more steps, either preceding step 210 or extending beyondthe steps that determine the position of conversion device bypass valve70. Thus, the flow chart shown in FIG. 4 is a reflection only of thegeneral nature of the steps that need to be accomplished to operate theelements of WHR system 100 shown in FIG. 2 rather than a comprehensivelist of all possible steps needed to operate an engine or all elementsof WHR system 100.

Returning now to step 212, if the estimated conversion device power isless than a maximum threshold valve, as determined using informationfrom sensors 84 associated with conversion device 46, then the processmoves to step 220, where the level of liquid working fluid 54 incondenser 20 and sub-cooler 18 is measured by using information fromworking fluid level sensor 62. The process then moves to decision step224. If the level of working fluid 54 in condenser 20 and sub-cooler 18is less than a minimum threshold level, then the process moves to step226. At step 226, control module 80 commands conversion device bypassvalve 70 to the second position. As previously described, in the secondposition conversion device bypass valve 70 connects conversion devicebypass conduit 68 with receiver conduit 74. A portion of thehigh-pressure vaporized working fluid from boiler heat exchanger 34 willthen flow to receiver 126, forcing liquid working fluid 54 through diptube 52 into dip tube conduit 56. Liquid working fluid 54 then flowsthrough shutoff valve 58 and then shutoff valve conduit 60. Liquidworking fluid 54 then flows into base plate 222 and then flows intosub-cooler 18, restoring the level of liquid working fluid 54 to adesired level.

While the conversion device bypass valve 70 is causing the flow ofliquid working fluid 54, the process moves to step 216 where the processdetermines whether WHR system 100 is continuing to operate. As before,if WHR system 100 is shutting down, then the process will terminate. IfWHR system 100 is continuing to operate, then the process returns tostep 100. Eventually, decision step 224 will indicate that the level ofliquid working fluid 54 has reached a minimum threshold level insub-cooler 18 and condenser 20. When that happens, the process moves tostep 228.

At step 228, control module 80 receives the temperature of liquidworking fluid 54 at the inlet of pump 30 from sensors 82, which definesT_(pump). The process then moves to step 230, where control module 80refers to a “fluid saturation table” to determine the saturationpressure corresponding to T_(pump), which defines P_(fluid saturation).The process then moves to step 232. At step 232, control module 80receives the inlet pressure of liquid working fluid 54 at pump 30 fromsensors 82, which defines P_(pump). The process then moves to decisionstep 234. At decision step 234 a comparison is made between P_(pump) andP_(fluid saturation). P_(pump)<P_(fluid saturation), then the processproceeds to step 226 to move conversion device bypass valve 70 to thesecond position. This comparison may be modified by ΔP, which is thecavitation margin for WHR system 100, particularly for pump 30. Thecomparison would then be P_(pump)<P_(fluid saturation)+ΔP. The operationof the process at step 226 and the effect of conversion device bypassvalve 70 being in the second position has been discussed hereinabove.

Returning to decision step 234, if the process determines thatP_(pump)<P_(fluid saturation)+ΔP is not true, then the process proceedsto step 236. At step 236, control module 80 moves conversion devicebypass valve 70 to the first position. In the first position, which islikely to be the most common or typical position for conversion devicebypass valve 70, conversion device bypass valve 70 connects receiverconduit 74 with vent and bypass conduit 76. The process then moves todecision step 216, which operates as previously described.

Thus, this disclosure describes a system and method that uses a gravitydrain low mount receiver 126 in a Rankine cycle or an organic Rankinecycle. High vapor pressure regulates the level of liquid working fluid54 in condenser 20 and sub-cooler 18 by forcing liquid working fluid 54from receiver 126 to condenser 20 and sub-cooler 18 when needed withoutthe need for a pump in receiver 126. The conversion device bypass valve70 has a combined functionality that includes regulation of theinventory of liquid working fluid 54 in receiver 126 and power limitingof conversion device 46. This configuration solves packaging concernsrelated to receiver 126 in mobile applications, though the benefits ofthe present disclosure may apply to stationary applications as well.

While various embodiments of the disclosure have been shown anddescribed, it is understood that these embodiments are not limitedthereto. The embodiments may be changed, modified and further applied bythose skilled in the art. Therefore, these embodiments are not limitedto the detail shown and described previously, but also include all suchchanges and modifications.

1. A fluid management system for a Rankine cycle waste heat recoverysystem for an internal combustion engine, the fluid management systemcomprising: a fluid circuit; a condenser positioned along the fluidcircuit; a sub-cooler fluidly connected to the condenser and containinga liquid working fluid; a receiver fluidly connected to the sub-coolerand containing the liquid working fluid, wherein a level of the liquidworking fluid in the receiver is lower than a level of the liquidworking fluid in the sub-cooler throughout all operating conditions. 2.The system of claim 1, further including a valve positioned along thefluid circuit upstream of the condenser and movable into a firstposition and a second position; wherein the valve second positionfluidly connects a source of high-pressure vaporized working fluid tothe receiver; and wherein the high-pressure vaporized working fluidcauses the liquid working fluid in the receiver to flow from thereceiver to the sub-cooler.
 3. The system of claim 1, further includinga pump fluidly connected to the sub-cooler and connected to at least oneheat exchanger, wherein the pump is operable to move the liquid workingfluid in the sub-cooler to the at least one heat exchanger.
 4. Thesystem of claim 3, wherein the at least one heat exchanger is the sourceof the high-pressure vaporized working fluid.
 5. The system of claim 3,wherein the at least one heat exchanger receives exhaust gas from anexhaust gas recirculation system.
 6. The system of claim 4, wherein theat least one heat exchanger heats the liquid working fluid and changesthe state of the liquid working fluid to the high-pressure vaporizedworking fluid.
 7. The system of claim 2, wherein the valve firstposition fluidly connects the receiver to the condenser.
 8. The fluidmanagement system of claim 2, wherein the valve includes a thirdposition and the valve third position connects the source ofhigh-pressure vaporized working fluid to the condenser.
 9. The system ofclaim 1, wherein the receiver is physically located in a position thatis lower than the sub-cooler's position.
 10. A waste heat recoverysystem for an internal combustion engine, the waste heat recovery systemcomprising: a working fluid circuit, including: a cooled condenserreceiving a vaporized working fluid and operable to change the state ofthe vaporized working fluid to a liquid working fluid; a sub-coolerfluidly connected to the condenser and receiving the liquid workingfluid; a pump fluidly connected to the sub-cooler and operable to movethe liquid working fluid from the sub-cooler; a heat exchanger fluidlyconnected to a pump to receive the liquid working fluid and operable totransfer heat from a heat source to the liquid working fluid to convertthe liquid working fluid to the vaporized working fluid, wherein thevaporized working fluid is at a high pressure; and an energy conversiondevice fluidly connected to the heat exchanger and operable to convertthe high-pressure vaporized working fluid received from the heatexchanger to energy; and a fluid management circuit fluidly connected tothe working fluid circuit, the fluid management circuit including: aconversion device bypass valve fluidly connected to the heat exchangerin parallel to the energy conversion device; and a receiver fluidlyconnected to the conversion device bypass valve, wherein the receiver isplaced at a physical location where the maximum liquid working fluidlevel in the receiver is lower than the minimum liquid working fluidlevel in the condenser and the sub-cooler; wherein the conversion devicebypass valve is operable to fluidly connect the heat exchanger to thereceiver, simultaneously disconnecting a direct path to the condenserfrom the heat exchanger and the receiver; and wherein vaporized workingfluid flowing from the heat exchanger forces the liquid working fluid toflow from the receiver to the sub-cooler.
 11. The waste heat recoverysystem of claim 10, wherein the position of the receiver is physicallylower than the position of condenser and the sub-cooler.
 12. The wasteheat recovery system of claim 10, wherein the conversion device bypassvalve is alternatively operable to connect the receiver to the condenserfluidly, simultaneously blocking fluid connections through theconversion device bypass valve to the heat exchanger.
 13. The waste heatrecovery system of claim 10, wherein the conversion device bypass valveis alternatively operable to connect the heat exchanger to thecondenser, simultaneously blocking fluid connections through theconversion device bypass valve to the receiver.
 14. The waste heatrecovery system of claim 10, wherein the heat exchanger receives exhaustgas from an exhaust gas recirculating system.
 15. The waste heatrecovery system of claim 10, further including a control module, whereinthe control module monitors the liquid working fluid level in thesub-cooler and commands the conversion device bypass valve to be in theposition that fluidly connects the heat exchanger to the receiver whenthe level of the liquid working fluid in the sub-cooler is less than alevel established by a process stored within the control module.
 16. Thewaste heat recovery system of claim 10, further including a controlmodule, wherein the control module monitors the temperature and pressureof the liquid working fluid flowing to the pump and wherein when thepressure of the liquid working fluid flowing to the pump is less than afluid saturation pressure determined by the temperature of the liquidworking fluid flowing to the pump the control module commands theconversion device bypass valve to move to a position that fluidlyconnects the heat exchanger to the receiver.
 17. A valve configurationfor a Rankine cycle waste heat recovery system, the valve configurationcomprising: a heat exchanger, wherein the heat exchanger is a source ofvaporized working fluid; a condenser; a sub-cooler fluidly connected tothe condenser; a receiver fluidly connected to the sub-cooler; and avalve; wherein the valve has a first position such that the valvefluidly connects the receiver to the condenser; wherein the valve has asecond position such that the valve fluidly connects the heat exchangerto the receiver; and wherein the valve has a third position such thatthe valve fluidly connects the heat exchanger to the condenser.
 18. Thevalve configuration of claim 17, wherein the heat exchanger receives anexhaust gas from an exhaust gas recirculation system.
 19. The valveconfiguration of claim 17, wherein the receiver contains a liquidworking fluid and wherein when the valve is in the second position, thevalve directs vaporized working fluid to the receiver, forcing liquidworking fluid contained within the receiver through a conduit into thesub-cooler.
 20. The valve configuration of claim 17, wherein thereceiver has a physical location that is lower than the position of thesub-cooler.
 21. A waste heat management system, comprising: a sub-coolercontaining a liquid working fluid, wherein the liquid working fluid inthe sub-cooler has a first level; a receiver fluidly connected to thesub-cooler and containing the liquid working fluid, wherein the liquidworking fluid in the receiver has a second level; and a valve fluidlyconnected to the receiver; wherein the first level is higher than thesecond level; and wherein the valve is selectively operable to delivervaporized working fluid to the receiver to apply pressure to the liquidworking fluid in the receiver to force the liquid working fluid in thereceiver to flow into the sub-cooler.
 22. The waste heat managementsystem of claim 21, further comprising a heat exchanger, wherein thepressure is from vaporized working fluid received from the heatexchanger.
 23. A method of controlling fluid flow through a waste heatrecovery system, the method comprising: generating vaporized fluid in aworking fluid circuit from a liquid working fluid located in the workingfluid circuit, wherein the liquid working fluid has a level; providingthe vaporized fluid to a working fluid management circuit connected inparallel to the working fluid circuit; determining that the level of theliquid working fluid in the working fluid circuit is different from anoperationally desirable level; allowing the vaporized fluid to flowthrough the working fluid management circuit to force liquid workingfluid in the working fluid management circuit to flow from the workingfluid management circuit into the working fluid circuit, to change thelevel of the liquid working fluid in the working fluid circuit; andterminating the flow of vaporized fluid through the working fluidmanagement circuit when the liquid working fluid in the working fluidcircuit has reached an operationally desirable level.
 24. The method ofclaim 23, wherein the working fluid management circuit includes areceiver and wherein the working fluid circuit includes a condenser anda sub-cooler, and the liquid working fluid moves between the receiverand the condenser, and the sub-cooler.
 25. The method of claim 24,wherein the receiver is positioned so that the maximum level of theliquid working fluid in the receiver is lower than minimum level of theliquid working fluid in the condenser and the sub-cooler.
 26. The methodof claim 25, wherein the receiver is physically positioned lower thanthe condenser and the sub-cooler.
 27. The method of claim 23, whereinthe vaporized fluid is selectively applied to the working fluidmanagement circuit by a valve.